Assessment of Prospective CYP2C19 Genotype Guided Dosing of Anti-Platelet Therapy in Percutaneous Coronary Intervention

Clopidogrel is a thienopyridine antiplatelet agent, which inhibits the purinergic P2RY12 receptor on platelets and prevents their aggregation. It is commonly used in patients with acute coronary syndromes (ACS) undergoing percutaneous coronary intervention (PCI). CYP2C19 is one of the principal enzymes involved in the bioactivation of clopidogrel from the pro-drug to its active metabolite. The most common loss of function (LOF) allele is *2 (c.681G>A; rs4244285), with frequencies of ~15% in Caucasians and Africans and 29-35% in Asians. A large meta-analysis demonstrated that CYP2C19*2 carriers treated with clopidogrel have a higher risk for major adverse cardiac events compared to noncarriers.Therefore, clopidogrel is less effective in patients who are CYP2C19 poor metabolizers and alternative therapy is recommended. A newer-generation thienopyridine, prasugrel, was found to be associated with a reduction in major adverse cardiac events (death, myocardial infarction, stroke) compared to clopidogrel, but with an increased risk of fatal and major bleeding events.

Now that clopidogrel is available in generic form, pharmacogenetic (PGx) screening could allow for individualized anti-platelet therapy in which patients with functional CYP2C19 alleles could be prescribed clopidogrel, and the more expensive agent would be reserved for patients with poor metabolizer status. A cost-effectiveness analysis of CYP2C19 screening for selection of antiplatelet therapy found that genotype-guided therapy would lead to more cost-effective care rather than uniform usage of either clopidogrel or prasugrel.

A more recent economic evaluation determined that genotyping and prescribing ticagrelor to LOF allele carriers was the most effective strategy when compared against routine clopidogrel or prasugrel use as well as genotyping and prescribing prasugrel to LOF carriers. However, these results were based on decision model of a hypothetical cohort of patients with ACS who underwent PCI and several assumptions were made regarding outcomes, cost and quality of life. True costs associated with genotype guided antiplatelet therapy are unknown. Future prospective studies evaluating the cost effectiveness of a genotype guided approach are needed. We are proposing a pilot study which will provide information necessary for planning a prospective study that will directly estimate events averted, costs, quality-adjust life years (QALYs) and cost per QALY ratios. Information to be obtained in this pilot includes estimates of costs and their variance, preference scores (for calculating QALYs) and their variance, the correlation of cost and effects (required for sample size estimation for cost-effectiveness ratios), event rates, and implementation metrics (to estimate likely penetration of testing in the trial). The results from this study will provide more accurate estimates of the means and variances of cost and QALYs required to plan future trials.

OBJECTIVES

• To identify factors linked with successful implementation of clinical pharmacogenetic (PGx) testing in a large academic medical center.
• To conduct a prospective pilot study to determine means and variances for cost, QALYs and the correlation of cost and effect.
• To determine the rates of clinical outcomes.

APPROACH In the genotype guided arm, a buccal swab will be obtained from subjects immediately following PCI/stent, to determine CYP2C19 genotype with the SpartanRx system. Subject with slow metabolizer status [1 or 2 loss-of-function (LOF) mutations (*2 or *3) in CYP2C19] will be recommended to initiate therapy with prasugrel or ticagrelor in place of clopidogrel. Subjects with normal metabolizer status (homozygous for the *1 allele in CYP2C19) will be recommended to initiate therapy with clopidogrel. Antiplatelet choice is ultimately decided by physician judgment incorporating all clinical factors.

In the control arm, choice of antiplatelet therapy will be decided by treating physician as per usual care. DNA will be collected via a saliva sample to assess CYP2C19 genotype at the conclusion of the study.

Subjects in both groups will complete a baseline health related quality of life questionnaire (HrQoL) and additional clinical data pertaining to cardiac history will be collected from medical records. Subjects will be contacted every three months for medical services utilization, clinical information, and HrQoL assessments for a total of one year.